The engine is a little Yanmar diesel, again no light weight.
Not realizing how heavy the head would get I used 4 inch channel on the flat for the base. Im guessing the head is about 1000 pounds, judging from how the tractor lifts it. Started sawing some beams last week and noticed the blade diving a little, something it doesn't normally do with a sharp blade.
Started looking for problems with the guides but found the base had sagged.
You can see the end bent up about an inch, with the back framework, that would case the head to tilt forward and make the blade want to dive.

The Moment of Inertia for the channel, in the plane its loaded is only 0.289 in4. Im replacing it with 5x5x3/8 angle I had. Its Moment of Inertia is 8.76 in4 making the member about 30 times stiffer.

f350ca

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Far too many projects on the go. Finally got back to this. A cutoff disk on the 7 inch angle grinder made a clean cut separating the carriage. The new base sections were blocked at one end and levelled using a machinist jack and precision level. The top frame was positioned and angle blocks clamped to the uprights, these gave a base for the level to get it plumb. Turnbuckles and chains were used to adjust the position.

f350ca

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Thanks Paco. Should stop the sag. Re-inventing the blade guide adjustments now. Had never used a mill till I built this one so a few things could be improved. I mounted the moveable guide on a slide that requires loosening a couple of bolts, large movements require moving to another set of holes. Seams moving the guide happens more than I thought so we're building a new system while its in the shop.